Angioplasty has become an accepted and rapidly expanding method for the treatment of certain types of vascular disease. In percutaneous transluminal angioplasty, a guide wire is introduced percutaneously into the patient's vascular system and advanced and steered to the site of the stenosis. A dilation catheter is then advanced over the guide wire until it is positioned at the stenosis site so that it can be inflated to dilatate the artery and reestablish a more adequate blood flow path therethrough.
Such techniques are especially important in the treatment of coronary artery diseases by percutaneous transluminal coronary angioplasty. In coronary applications, guide catheters, guide wires and angioplasty catheters have been specially developed for maneuvering through numerous arterial branches and into the particular coronary artery branch where treatment is desired. Because of the many branches which must be successfully negotiated and the convoluted, tortuous path which must be followed by the catheter, numerous specialized instruments have been developed for this purpose, with the result that an increasingly large number of cases can be successfully treated. However, certain problems still can be encountered in the positioning of the angioplasty catheter, especially in the final few tight branches an turns leading to a stenosis site in a coronary artery. The problem can occur after a guide wire has successfully been advanced into position and while the dilatation catheter is being advanced over the guide wire. When encountering a sharp turn to a smaller artery, it is possible that the distal end of the dilatation catheter may be too stiff to make the small radius turn. This can cause great difficulty in trying to manipulate and maneuver the catheter around the turn, and in extreme cases can result in the catheter actually advancing down the wrong branch and pulling the guide wire out of the intended branch.
Prior art catheters tend to have a relatively stiff shaft which transitions at the beginning of the balloon to a lower stiffness. This means that the flexible distal portion of a prior art catheter consists only of the relatively small tip and the balloon, with the stiffer shaft starting immediately adjacent the balloon. This may not provide sufficient flexibility to permit the catheter to follow sharp bends, and may result in the stiff shaft pushing the balloon past the branch and even pulling the guide wire out of the branch.
An alternate construction in the prior art uses a central lumen defining tube, and an outer, relatively flexible tube which forms the shaft and which has the balloon formed integrally therewith at the end. While this type of construction provides great flexibility for following sharp bends, after a number of such bends have been encountered, the shaft is too soft to transmit sufficient axial force without buckling, and it becomes impossible to advance the catheter any farther.